xylem

Xylem is a vascular tissue that distributes water and solutes throughout the body of a plant. It is found continuously in the plant, passing through all the organs and forming a true circulation network of substances. In addition to ensuring the transport of substances, the xylem acts in the mechanical support of the plant and in the storage of substances.

→ Origin of the xylem

Xylem is a conducting tissue found in the plant body in primary and secondary growth. Xylem is called primary when it is formed from the procambium (primary meristematic tissue) and is called secondary when it is formed from the vascular cambium (secondary or lateral meristem).

Primary xylem can also be distinguished from secondary xylem through the organization of its components. While the primary xylem is organized only in the axial (vertical) system, the secondary xylem is organized in an axial and radial (horizontal) system.

→ Main features of xylem

Xylem is a complex tissue, that is, it is formed by more than one cell type. The conductive elements, parenchyma cells and fibers are part of the xylem constitution.

Conductive elements or tracheal elements can be divided into two basic groups: tracheids and vessel elements. These two cell groups stand out because they are not alive at maturity, have secondary cell walls, have pits (a place where the secondary wall is not deposited) and have water conduction as their main function.

The difference between the tracheal elements is in the fact that the tracheids are imperforate, and the vessel elements have the perforation plates. These drill plates have holes that ensure a continuous flow of substances. The elements of vases are arranged in the plants forming long columns, thus constituting true vases.

The parenchyma cells present in the xylem act, mainly, ensuring the storage of various substances, but they can also carry out water and solute transport over short distances. Fibers are also cells that make up the xylem, and their role is to ensure support . They are elongated, tapered at the tip, and have thickened cell walls. Fibers can be classified into libriform and fibrotracheid.

Libriform fibers are distinguished from fibrotracheids by the type of pitting. While libriform fibers have simple pits characterized only by the interruption of the secondary wall, fibrotracheids have areolated pits, which, when viewed from the front, resemble an areola.